Phase-Transfer Catalysis
Phase-transfer catalysis (PTC) facilitates reactions between substances in different phases of a reaction medium. One or more of the reactants are organic liquids or solids dissolved in a water insoluble organic solvent and the coreactants are salts or alkali metal hydroxides in aqueous solution. In the absence of a phase-transfer catalyst the reactions are often slow or non-existent; in its presence the conversions occur rapidly and efficiently. Examples of such catalysts known in the art include onium compounds, e.g. quaternary ammonium or phosphonium salts, and crown ethers and cryptates. PTC is used for a wide variety of reactions including anion exchange; nucleophilic addition; nucleophilic substitution; reduction; alkylations of weak C-H acidic compounds up to a pK.sub.a limit of 22-25; alkylations of ambident anions; alkylations of OH, NH, and SH bonds; isomerizations and H-D-exchange; additions across C.dbd.C and C.dbd.O bonds; .beta.-eliminations; formation of carbenes by .alpha.-eliminations; hydrolysis and saponifications; Darzens reactions; Horner-Wittig reactions; oxidations, e.g. olefins to carboxylic acids; and reactions of sulfonium ylides.
Normally the above reactions are performed in homogenous media. However, the use of hydroxylic solvent alone results in the solvation of anion reactants which hinders the desired conversion reactions. Accordingly, expensive dipolar aprotic solvents are utilized to effect such reactions in a homogeneous environment. In contrast, carrying out these reactions by PTC avoids the need for such expensive solvents while simplifying workup, reducing reaction time and reaction temperatures. PTC is further advantageous in its use of aqueous alkali hydroxides as a substitute for more expensive bases. Additional information concerning PTC is found in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 5, pp. 62 to 69, John Wiley & Sons, New York (1979), the contents of which are incorporated herein by reference.
Despite the advantages of PTC, common phase-transfer catalysts such as the onium compounds are soluble in water and thus difficult to reclaim from reaction media. To avoid such difficulties efforts have been made to provide phase transfer catalysts immobilized on a substrate. The use of such materials in PTC affords processing advantages such as simple filtration of the catalyst as well as its use in recycle and fixed bed applications. P. Tundo, et al., JCS Chem. Comm, p. 641 1977 discloses the immobilization of phase transfer catalysts on silica and alumina by reacting surface hydroxyls with .OMEGA.-bromoalkyltriethoxysilicates, e.g. Br(CH.sub.2).sub.3 SiOCH.sub.2 CH.sub.3, then quaternizing with either tertiary phosphine or amines. P. Tundo, et al., J. Am. Chem. Soc. 1982 104, 6551 discloses a method which modifies silica and alumina by reacting surface hydroxyls with .OMEGA.-amino alkyltriethoxysilicates, e.g. H.sub.2 N(CH.sub.2).sub.3 Si(OCH.sub.2 CH.sub.3).sub.3, followed by amidation with .OMEGA.-bromoalkylacid chlorides, then quaternizing with either tertiary phosphine or amines.
PTC using cetyltrimethylammonium is disclosed in U.S. Pat. No. 3,992,432, the entire contents of which being incorporated herein by reference.
Synthetic ultra-large pore non-layered crystalline materials can be prepared from a reaction mixture which utilizes onium compounds, e.g., cetyltrimethylammonium hydroxide, as a directing agent.
Applicants know of no prior art teaching the presently claimed use of synthetic ultra-large pore non-layered crystalline materials in phase-transfer catalysis.